push sheeet

nixos/modules/system/boot/loader/external/external.md

@@ -0,0 +1,27 @@
+# External Bootloader Backends {#sec-bootloader-external}
+
+NixOS has support for several bootloader backends by default: systemd-boot, grub, uboot, etc.
+The built-in bootloader backend support is generic and supports most use cases.
+Some users may prefer to create advanced workflows around managing the bootloader and bootable entries.
+
+You can replace the built-in bootloader support with your own tooling using the "external" bootloader option.
+
+Imagine you have created a new package called FooBoot.
+FooBoot provides a program at `${pkgs.fooboot}/bin/fooboot-install` which takes the system closure's path as its only argument and configures the system's bootloader.
+
+You can enable FooBoot like this:
+
+```nix
+{ pkgs, ... }:
+{
+  boot.loader.external = {
+    enable = true;
+    installHook = "${pkgs.fooboot}/bin/fooboot-install";
+  };
+}
+```
+
+## Developing Custom Bootloader Backends {#sec-bootloader-external-developing}
+
+Bootloaders should use [RFC-0125](https://github.com/NixOS/rfcs/pull/125)'s Bootspec format and synthesis tools to identify the key properties for bootable system generations.
+

nixos/modules/system/boot/loader/external/external.nix

@@ -0,0 +1,45 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+with lib;
+
+let
+  cfg = config.boot.loader.external;
+in
+{
+  meta = {
+    maintainers = with maintainers; [
+      cole-h
+      grahamc
+      raitobezarius
+    ];
+    doc = ./external.md;
+  };
+
+  options.boot.loader.external = {
+    enable = mkEnableOption "using an external tool to install your bootloader";
+
+    installHook = mkOption {
+      type = with types; path;
+      description = ''
+        The full path to a program of your choosing which performs the bootloader installation process.
+
+        The program will be called with an argument pointing to the output of the system's toplevel.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    boot.loader = {
+      grub.enable = mkDefault false;
+      systemd-boot.enable = mkDefault false;
+      supportsInitrdSecrets = mkDefault false;
+    };
+
+    system.build.installBootLoader = cfg.installHook;
+  };
+}